Another report:
It is soundly recorded in the two Ṣaḥīḥs, through the chain of Abū al-Naḍr Hāshim ibn al-Qāsim, from Waraqāʾ ibn ʿUmar al-Sukkarī, from ʿAbd Allāh ibn Yazīd, from Ibn ʿAbbās, who said:
“The Messenger of Allah ﷺ went to relieve himself, so I placed water for his wuḍūʾ. When he came out he asked, ‘Who put out this water?’ They said, ‘Ibn ʿAbbās.’ He replied, ‘O Allah, grant him deep understanding of the religion.’” (1)

Al-Bayhaqī also related—via al-Ḥākim and others—from al-Aṣamm, from ʿAbbās al-Dawraqī, from al-Ḥasan ibn Mūsā al-Ashayb, from Zuhayr, from ʿAbd Allāh ibn ʿUthmān ibn Khuthaym, from Saʿīd ibn Jubayr, from Ibn ʿAbbās that:
“The Messenger of Allah ﷺ placed his hand upon my shoulder—or he said, ‘upon my upper arm,’ Saʿīd was unsure—then said, ‘O Allah, grant him understanding of the religion and teach him the interpretation (of Your Book).’” (2)

Allah answered His Messenger’s ﷺ supplication for his cousin. Ibn ʿAbbās became an imām whose guidance was sought and whose radiant example was followed in the sciences of the Sharīʿah—especially in the science of tafsīr, for the knowledge of the Companions converged in him along with what he himself had grasped from the words of his cousin, the Messenger of Allah ﷺ.

Al-Aʿmash narrated—from Abū al-Ḍaḥḥāʾ (3), from Masrūq—that ʿAbd Allāh ibn Masʿūd said: “Had Ibn ʿAbbās reached our age, none of us would have equaled one-tenth of him,” and he used to say to them, “What an excellent interpreter of the Qur’an Ibn ʿAbbās is!” (4)

Ibn ʿAbbās actually outlived ʿAbd Allāh ibn Masʿūd by some thirty-odd years, so imagine what he acquired in that span of time!

It is also related from one of his students that Ibn ʿAbbās addressed the people on the afternoon of ʿArafah and explained Sūrat al-Baqarah—or, he said, another sūrah—in such detail that, had the Romans, the Turks, and the Daylamites heard it, they would have embraced Islam. (5) May Allah be pleased with him and grant him His good pleasure.